Cobalt-tungsten high temperature eutectic alloy

ABSTRACT

A directionally solidified alloy body having a matrix consisting essentially of a metallic solid solution of cobalt containing therein a cobalt-tungsten intermetallic compound as a reinforcing phase. The high temperature (1800*F) ultimate tensile strength of the body is in excess of 90 KSI, with about 7% elongation.

United States Patent Buchanan et a1.

[ COBALT-TUNGSTEN HIGH TEMPERATURE EUTECTIC ALLOY [75] Inventors: Edward R. Buchanan, Burnt Hills;

Lemuel A. Tarshis, Latham, both of NY.

[73] Assignee: General Electric Company,

Schenectady, NY.

[22] Filed: July 16, 1971 [21] Appl. No.: 163,290

52 U5. C1 .L 75/170; 75/135 [51] Int. Cl. C22C 19/07 [58] Field of Search: 75/170, 135

[56] References Cited UNITED STATES PATENTS 3,124,452 3/1964 Kraft 75/135 Dec. 23, 1975 3,271,140 9/1966 Freche et a1 75/170 3,434,827 3/1969 Lemkey 75/135 X 3,434,892 3/1969 Heimke 148/1.6 X 3,564,940 2/1971 Thompson et al. 75/135 X OTHER PUBLICATIONS Elliott, R. P., Constitution of Binary Alloys McGraw-l-lill Book Co., 1965, p. 342.

Primary ExaminerA1len B. Curtis Attorney, Agent, or FirmF. Wesley Turner; Joseph T. Cohen; Jerome C. Squillaro [57] ABSTRACT A directionally solidified alloy body having a matrix consisting essentially of a metallic solid solution of cobalt containing therein a cobalt-tungsten intermetallic compound as a reinforcing phase. The high temperature (1800F) ultimate tensile strength of the body is in excess of 90 KS1, with about 7% elongation.

4 Claims, 3 Drawing Figures U.S. Patent Dec. 23, 1975 Sheet 1 of2 3,928,030

FIG. 2

EDWARD BUCHANAN LEMUEL A. TARSH/S THE/f? ATTORNEY U.S. Patent Dec. 23, 1975 Sheet 2 of2 3,928,030

DIRECTIONALLY SOL. hr.) II I! lnhr.) 0 A5 0437 I40- a 3 CAST R80 E E EIOO- 0 I 5', E k so E E 60 S 0 200 J\/ I000 I200 I400 I600 I800 2000 TEMPERATURE (7-7 //V VE/V TOPS.

EDWARD R. BUCHANAN LEMUEL A. TARSH/S THE If? ATTORNEY COBALT-TUNGSTEN HIGH TEMPERATURE EUTECTIC ALLOY alloys have utility in gas turbine engine components subject to high temperatures of about l800F under highly corrosive conditions. I

A principle object of the present invention is to provide a cobalt-tungsten alloy article prepared by directional solidification, which in addition to adequate ductility has high tensile strength at room temperature and when subjected to elevated temperatures.

Another object of the invention is to provide a cobalt-tungsten alloy which will contain in excess of by volume of an intermetallic compound which imparts to the alloy good tensile properties while maintaining adequate oxidation resistance.

These and other objects and advantages of the invention will be more fully recognized and appreciated from the following detailed description including the drawings and representative examples which are typical of the present invention.

In the drawings:

FIG. 1 is a chart plotting ultimate tensile strength in KSI vs. temperature in F, comparing a preferred alloy of the present invention with a known nickel-base supperalloy, Ren 80; FIG. 2 is a photomicrograph (l50 illustrating a longitudinal section of a cobalt-tungsten alloy body according to the invention directionally solidified at a rate of 1 inch per hour; and

FIG. 3 is a photomicrograph (l50X) showing a transverse section through the alloy body of FIG. 2.

Table I below lists the ultimate tensile strength and elongation of a cobalt-tungsten alloy according to the invention directionally solidified at different rates, as compared to the corresponding as-cast alloy at room temperature.

TABLE I Ultimate Temperature Tensile Strength ElongationWr F) (KSI) CoW 75 102.7 l.() as cast Co-W 75 204 L6 Directionally solidified (W'lhour) I800 92 7.8 Co-W 75 I87 1.0 Directionally increase in elongation over the as-cast condition, as well as a substantial increase in ultimate tensile strength.

As may be seen in the photomicrographs of FIGS. 2 and 3, the microstructure of the directionally solidified ingots of the nominal alloy containing, by weight, 55% cobalt and 45% tungsten, forms two phases. The matrix or primary phase is cobalt solid solution containing tungsten in solution therein. The second phase, which is the reinforcing phase, appears as a broken lamellar array. This reinforcing phase is an intermetallic compound corresponding approximately to Co W As is true in general for eutetic alloys, the cobalt and tungsten constituents need not be present in exactly stoichiometric proportions in the intermetallic compound, and may contain, at equilibrium, an excess or a deficiency of cobalt, the other phase which makes up the eutectic.

The reinforcing phase of the cobalt-tungsten intermetallic compound forms a volume fraction of from 20 to 25% in the matrix.

EXAMPLE I As a preferred example, a nominal composition consisting of 55 wt. cobalt and 45 wt. tungsten was melted and cast into an ingot. This ingot was remelted and directionally solidified in a Bridgman apparatus at a rate of /z inch/hour in a temperature gradient of about l0OC/cm.

EXAMPLE II A composition similar to that of Example I was directionally solidified at l inch/hour in the same apparatus.

The physical properties of the two examples are shown in Table I above.

To the simple binary eutectic of cobalt and tungsten one may also add other elements which will go into solid solution into each of the two phases of the eutectic, namely into the intermetallic compound phase and into the cobalt solid solution phase. The resulting cobalt-base alloy may contain, in solid solution in each of the two phases of the Co-Co,W, eutectic, at least one of the elements: chromium, nickel, aluminum, molybdenum, iron, titanium and yttrium as solutes up to the limit of solid solubility of the respective element in the respective phase of the eutectic in which said element is least soluble.

EXAMPLE III Oxidation resistance of a 55 w/o cobalt-45 w/o tungsten eutectic alloy directionally solidified at /2 inch/- hour was determined by heating a specimen at l 100C for 15 hours, together with a specimen of a known nickel-base superalloy Rene for comparison purposes. The results showed that the nickel-base alloy exhibited gross spalling upon cooling. The resulting oxide film on the cobalt-tungsten specimen was dense and adherent, and no spalling occurred on cooling.

It will be obvious to those skilled in the art upon reading the foregoing disclosure that many modifications and alterations in the specific compositions and microstructures disclosed non-limiting examples may be made within the general context of the invention, and that numerous modifications, alterations and additions may be made thereto within the true spirit and scope of the invention as set forth in the appended claims.

What we claim as new and desire to secure by Letters Patent of the U5. is:

l. A directionally solidified cast alloy body consisting essentially in weight percent of 5357% of cobalt and 43-47% of tungsten, said body having a reinforcing phase of an intermetallic compound having the approximate chemical composition Co W dispersed in a matrix phase of a cobalt-tungsten solid solution.

2. The body according to claim 1, said cobalt-tungsten intermetallic compound comprising form 20 to 25 volume 7: of said matrix.

3. The body according to claim 1, said cast body comprising a binary eutectic alloy of cobalt and tungsten containing, by weight, about 55.0% cobalt and about 45% tungsten. said body being characterized by its high temperature oxidation resistance and having an ultimate tensile strength at l800F. in excess of KSl.

4. The body according to claim 1, further containing in solid solution in each of the two phases of the binary eutectic alloy, an addition of at least one element selected from the group consisting of chromium, nickel, aluminum, molybdenum, iron, yttrium and titanium, said addition being present in an amount not to exceed the limit of solid solubility of said -one element in the phase of said eutectic in which said one element is least soluble. 

1. A DIRECTIONALLY SOLIDIFIED CAST ALLOY BODY CONSISTING ESSENTIALLY IN WEIGHT PERCENT OF 53-57% OF COBALT AND 43-47% OF TUNGSTEN, SAID BODY HAVING A REINFORCING PHASE OF AN INTERMETALLIC COMPOUND HAVING THE APPROXIMATE CHEMICAL COMPOSITION CO7W6 DISPERSED IN A MATRIX PHASE OF A COBALT-TUNGSTEN SOLID SOLUTION.
 2. The body according to claim 1, said cobalt-tungsten intermetallic compound comprising form 20 to 25 volume % of said matrix.
 3. The body according to claim 1, said cast body comprising a binary eutectic alloy of cobalt and tungsten containiNg, by weight, about 55.0% cobalt and about 45% tungsten, said body being characterized by its high temperature oxidation resistance and having an ultimate tensile strength at 1800*F. in excess of 90 KSI.
 4. The body according to claim 1, further containing in solid solution in each of the two phases of the binary eutectic alloy, an addition of at least one element selected from the group consisting of chromium, nickel, aluminum, molybdenum, iron, yttrium and titanium, said addition being present in an amount not to exceed the limit of solid solubility of said one element in the phase of said eutectic in which said one element is least soluble. 